By way of example, in the pump described in document FR 2 885 890, use is made of a resilient membrane constituting a check valve, the membrane being fitted on a support that is pieced by a feed channel and that acts as a seat configured in such a manner that the check valve is either pressed against the seat in order to block the liquid, or else is spaced apart from the seat in order to allow the liquid to pass. The membrane is mounted to slide in leaktight manner in a metering chamber of the pump in order to expel from the chamber the composition that has been stored temporarily in the chamber. For this purpose, the resilient membrane has a transverse wall forming a check valve that closes a feed orifice of the chamber, and a cylindrical skirt provided with one or two peripheral sealing lips in sliding contact with the inside wall of the metering chamber.
It is found that that resilient membrane can be difficult to make and assemble. It is important for the checkvalve-forming portion to be capable of taking up optimally both a composition-release configuration and a composition-blocking configuration. In other words, it is important for this checkvalve-forming portion to be in leaktight contact with a support in order to prevent the composition from passing in one direction so long as the membrane is not subjected to suction, and that as soon as it is subjected to a level of suction that is as small as possible, it is important for it to allow the composition to pass. Thus, the checkvalve-forming portion needs to present dimensions and a position that are as accurate as possible.